Well, the pronounciation trick usually works and you'll never see an n (ン) at the beginning of a word.Mostly I try to get everyone to look at the alignment of the short strokes.If they are vertical and align sort of to the left it's a shi シ and it they are more horizontal and align up towards the top then it's a tsu ツ.Or you could say low eyes smile is shi シ and higher eyed smile is tsu ツ.